Puzzles having a number of pieces, which have to be fitted together, are well known. In particular most people are familiar with "jigsaw" puzzles, in which a large number of interlocking pieces can be fitted together to make a recognisable two-dimensional picture or pattern. Jigsaw puzzle pieces are usually of a number of different shapes, and this together with the colour variation over a picture generally means that there is only one "correct" way to complete the puzzle, i.e. correct as to both picture and fitting of pieces. However certain special jigsaw puzzles are known in which, apart from those at the edges, the pieces are all the same shape so that only assessment of the picture/pattern can be used in deciding where each piece is to fit.